Intervertebral disc prosthesis and fitting tools

ABSTRACT

An intervertebral disc prosthesis designed to be substituted for fibrocartilaginous discs ensures a connection between the vertebra of the vertebra column or the end of the latter. The prosthesis includes a pair of plates spaced from each other by a nucleus. The prosthesis has increased stability by providing the nucleus with a translation or rotation stop, or by inducing an angular correction between its plates contacting vertebra, or a combination of these characteristics. The stop includes parts external to the nucleus and contact surfaces perpendicular to their contact directions.

[0001] The present invention concerns an intervertebral disc prosthesisdesigned to be substituted for fibrocartilaginous discs ensuringconnection between the vertebra of the vertebral column or the end ofthe latter.

[0002] The intervertebral discs are formed from a deformable butnoncompressible element called “nucleus pulposus” containingapproximately 80% water, surrounded by several elastic fibrous layersconverging to maintain the nucleus, absorb part of the forces applied tothe entire disc and stabilize the articulation. These elements may oftenbe broken down or damaged by compression, displacement or wear and tear,following shocks, infections, exaggerated forces or simply over time.

[0003] The breakdown of this articulation element may cause intense painand significant constraint in the patient. Beyond the surgery thatconsisted of blocking the deficient articulation and possibly purely andsimply removing the damaged disc, a therapeutic route for the lasttwenty or so years consists of surgically replacing the defective discwith a functional prosthesis. However, the use of such a prosthesisrequires a device that is not very cumbersome, that supports significantforces, or has a great sturdiness over time. Furthermore, the comfort ofthe patients already affected by great and acute pain makes it desirableto arrange for a prosthesis that most faithfully reproduces the naturalpossibilities of movements and at the same time ensures the beststability possibility to the spinal column that is sometimes alreadydamaged.

[0004] The use of such a prosthesis therefore crucially depends on thestability that it allows the spinal column, as much during movements asduring static forces or lengthy constant position.

[0005] A certain number of prostheses have been proposed with acompressible material base, with the goal of reproducing the kinematicsof natural movement while reproducing its components and theircharacteristics of shape or plasticity, as described in the patent FR 2124 815 which proposes a disc from elastomer material reinforced by atextile material. These devices present the drawback of a lifetime thatis often too limited and also suffer from drawbacks indeed due to thiselasticity. In fact, since the prosthesis is entirely compressible, aprogressive sliding of the prosthesis may be produced relative to thevertebra between which it is placed, which too often leads it to leaveits housing. The addition of anchoring pins does not allow sufficientremedy for this problem, because the micromovements permitted by thecompressibility of the material of the prosthesis also include avertical component, which too easily allows the pins to leave theirhousing with each movement.

[0006] Among the prostheses nor resting on the deformation of materials,a type of prosthesis frequently used is described by the patent DE 30 23353 and is formed of a nucleus with the shape of a biconvex lens formingarticulation between two plates each presenting a cavity with a shapeapproximately complementary to the nucleus in their centre and on theirperimeter a shoulder retaining this nucleus. This arrangement presentsthe advantage by comparison to a more limited ball-and-socket joint ofusing significant contact surface, which largely decreases the wear andtear.

[0007] To incline one with the other on one side, the plates arearticulated by their internal cavity on the edge of the nucleus of theside in question, but according to a rotation movement which, on theother side makes their edges move apart more than they were at rest.This separating has a tendency to detach the vertebral plates on whichthey are supported, which damages the surface of the vertebra at thesites where the plates have just anchored and again allows progressivedisplacement with risk of complete ejection of the prosthesis.

[0008] Another type of prosthesis described in patent FR 2 659 226consists of an upper plate presenting a concave face that comes to slideon a nucleus in the form of a segment of a sphere, this nucleus beingimmobilized in a cavity of the lower plate. In this case, the rotationis done more satisfactorily from the point of view of space of theplates, but the sliding of the upper plate on a sphere whose centre islocated on the exterior of the prosthesis also causes lateraldisplacement which may be harmful as much to the kinematics of movementas to the organs present in the vicinity.

[0009] A solution is proposed in the patent FR 2 730 159 in the form ofa nucleus presenting two spherical faces, oriented in the samedirection, and with different radius. The nucleus with cylindricalexterior slides on a convex surface belonging the lower plate and itselfpresents a convex surface on the top, on which the upper plate slides.Because the nucleus is movable horizontally, it is in a position to moveapart from one side when the plates approach the other. However, thisdevice presents the drawback of risking the complete ejection of thenucleus outside the prosthesis, this drawback also existing in thedevice described by the patent DE 30 23 353.

[0010] In the goal of limiting the risks of ejection of the nucleus, thepatents WO 00 53 127, as well as U.S. Pat. No. 5,401,269 and U.S. Pat.No. 4,759,766 propose to provide a translation stop, produced indifferent ways.

[0011] In certain variants, a translation stop is disclosed in the formof a relief protruding from one contact surface of the nucleus andmovable in a recess in the plate or inversely. This type of internalstop is therefore located on the interior of a contact or supportsurface between nucleus and plate, and therefore decreases the availablesurface considerably. This decrease in support surface increases thestresses undergone by the materials, therefore the risks of wear andtear or strain in creep or exceeding elastic limits. The separationbetween the support surface and housing receiving the stop may also riskmarking the piece which is supported above and damaging the latter.

[0012] In certain cases, such a central stop is provided with anoncircular shape, which in a certain extent allows the rotations of thenucleus to be limited relative to the plate that provides it. However,this noncircular forms additional constraint which again limits thesurface available for support. Furthermore, the angles of this shapethemselves form fragile zones, which only ensures low sturdiness to thisstop operation in rotation.

[0013] In other variants, a collar protrudes from the nucleus andsurrounds it in the space between the two plates. In its exterior partthis collar widens at a certain height along the axis of the spinalcolumn towards each of the plates, which forms two interior borders thatmay be supported on the exterior border of contact surfaces of thesesame plates. However, this type of external peripheral stop presentscertain drawbacks, in particular in terms of obstruction.

[0014] In fact, the configuration of this collar represents considerablevertical obstruction (along the spinal column axis) and the contactsurfaces of the plates must also present a certain height to be able tostop this collar in translation. Furthermore, the peripheral shape ofthis type of stop also occupies considerable radial space, in particularin a section plane where the spinal column presents the smallest width,as in sagittal plane. Given the limited space available in the disc, orintervertebral, space, this obstruction may occupy a space that would beuseful for the configuration of the rest of the prosthesis, which maylimit the results in terms of kinematics or reliability.

[0015] Moreover, this type of external peripheral stop requires anucleus with biconvex shape to be used, to allow for provision ofsufficient height for the contact surfaces of the plates to form anexterior border usable by this stop. Therefore, this type of stop isdifficult to produce for a nucleus presenting one or more concavesurfaces, while such forms of nucleus may allow the kinematics of theprosthesis to be made more comfortable with use by the patient.

[0016] In the case where the contact surfaces between nucleus and platesare not circular, such a collar may also be able to limit the clearancein rotation of the nucleus relative to the plates, for example byperipheral contact between two concentric ellipses and with differentradii. However, such contact is done according to a very tight anglebetween the surfaces being supported on each other, which makes theposition of this limit not very precise and increases the risks of wearand tear or blockage by clamping. Furthermore, the clearance in rotationpermitted by such kinematics is directly dependent on the clearancepermitted in translation, and may not be chosen independently of thelatter during design of the prosthesis.

[0017] A goal of the invention is to propose a prosthesis allowing thespinal column better stability by a greater precision and sturdiness inrelative positions of pieces that compose it.

[0018] This goal is reached by a vertebral prosthesis device accordingto claim 1.

[0019] Moreover to ensure stability of the spinal column after fittingsuch a prosthesis, the damages undergone by the spinal column because ofthe different pathologies leading to deciding to fit a prosthesissometimes make useful the re-establishing of stability or posture thatthe elasticity of the spinal column no longer allows to be provided.According to the pathologies and the history of the patient, it may thenbe indicated to induce a certain angular correction in the configurationof the intervertebral space for example in the sense of lordosis or thatof kyphosis.

[0020] Certain types of existing prostheses use a variation in thicknessof one of the plates to induce such a correction. Such a correction isnot however always very stable, in particular because the position ofsupports of the nucleus on the plates varies too much during movements.

[0021] Another goal of the invention is therefore to propose aprosthesis allowing the prosthesis better stability by there-establishment of posture adapted to the kinematics of movements thatit produces.

[0022] This goal is reached by a vertebral prosthesis device accordingto claim 5.

[0023] Additional developments of the invention are described in thedependent claims.

[0024] The invention with its characteristics and advantages will bemore clearly evident with reading the description made in reference tothe attached drawings in which:

[0025]FIG. 1 represents an exploded view in perspective of a prosthesisaccording to the invention, in a version including a convex lower plateand providing a central and annular stop;

[0026]FIG. 2 represents an exploded sectional view of a prosthesisdevice according to the invention in the same variant;

[0027]FIG. 3 represents an exploded sectional view of the prosthesisdevice according to the invention in a variant including a nucleus withflat lower surface and lower plate presenting an annular stop;

[0028]FIG. 4 represents an exploded sectional side view of theprosthesis device according to the invention in a variant including anucleus with concave lower face, an added block and a lower plate withannular stop;

[0029]FIG. 6a represents a sectional side view of the prosthesis deviceaccording to the invention in a variant with central, annular andincline stop, in maximum incline position;

[0030]FIG. 6b represents a sectional side view of a prosthesis accordingto the prior arts where the nucleus presents a fixed position;

[0031]FIG. 6c represents a sectional side view of a prosthesis accordingto the prior arts where the nucleus is movable and is ejected under theload during a force in the maximum incline position;

[0032]FIG. 5 represents a sectional exploded side view of the prosthesisdevice according to a variant including an added block allowing acentral stop to appear and a flat lower plate presenting an annularstop;

[0033]FIG. 7 represents a sectional side view of the prosthesis deviceaccording to a variant without annular stop and where the central stoppresents a vertical section in the form of a dovetail, in maximumincline position;

[0034]FIGS. 8a and 8 b represent sectional side views of the prosthesisdevice according to the invention according to a variant with inclinedaxis, including an annular stop and a central stop incorporated in thecontact surface supporting the nucleus, in the case of a single piecelower plate and an added block, respectively.

[0035]FIG. 8c represents a sectional side view in a sagittal plane ofthe prosthesis device according to the invention according to a variantwith a corrective nucleus presenting two faces in which the contactsurfaces are not parallel;

[0036]FIG. 9a represents a perspective view of the prosthesis deviceaccording to the invention according to a variant with two stopsexterior to the nucleus, held in a housing between pillars integral withthe lower plate;

[0037]FIG. 9b represents a perspective view of the prosthesis deviceaccording to the invention according to a variant with two stopsexterior to the nucleus, each holding a pillar integral with the lowerplate between its arms;

[0038]FIG. 10 represents a perspective view of a device according to theinvention for fitting such a prosthesis;

[0039]FIG. 11 represents a perspective view of a device according to theinvention for inserting such a prosthesis, in position during theintroduction laterally of the prosthesis between two vertebrae;

[0040]FIG. 12 represents a perspective view of an assembly tool with aninsertion guide according to an embodiment of the invention;

[0041]FIG. 13 represents a perspective view of a prosthesis according tothe invention, presented at the entrance of the insertion guide of theinvention;

[0042]FIG. 14 represents a perspective view of the instrumentationaccording to an embodiment of the invention when the prosthesis is readyto be impacted in the disc space.

[0043] A prosthesis according to the prior art disclosed by the patentFR 2 659 226, consisting of a concave upper plate (3AA) sliding on anucleus (2AA) presenting a spherical upper cap (23M) itself immobilizedin a housing of the lower plate (1AA), is represented in FIG. 6b; inhorizontal position and in maximum incline position. Because the centreof the sphere (csAA) providing the contact surface with the nucleus islocated outside this same upper plate (3AA), its incline is combinedwith considerable lateral displacement (dl). This displacement creates abreak in the continuity of the vertical profile of the vertebral columnwhich may hamper the overall functionality of the movement and riskdamaging the tissues surrounding the vertebrae, such as ligaments andspinal marrow, which may be immediately or in the long run.

[0044] A prosthesis according to the prior art disclosed by the patentFR 2 730 159, represented in FIG. 6c, consists of a movable nucleus withtwo spherical surfaces oriented in the same direction, that may belaterally displaced between two plates and may allow incline withoutlateral displacement. In the extreme position, however, the nucleus isonly kept on the exterior side by the furthest border of the sphericalsurface of the upper plate. Since this edge itself is already raised,there is a great risk that too high a vertical pressure or a horizontalparasitic force causes ejection of the nucleus towards the exterior ofthe prosthesis, causing intense pain and risks of immediate damage forthe tissues surrounding the vertebral column, such as ligaments orspinal marrow.

[0045] In an embodiment represented in FIG. 6a, a prosthesis accordingto the invention consists of a lower plate (1) being articulated with anupper plate (3) around a nucleus (2) presenting two spherical slidingsurfaces with the same orientation on both faces. The lower surface (21)of the nucleus (2) is concave and slides on a complementary convexsurface (12) provided by the upper face, known as internal, of the lowerplate (1). The upper surface (23) is convex and slides on acomplementary concave surface (32) provided by the lower face, known asinternal, of the upper plate (3). In this embodiment, the radius of thelower contact surface (21) of the nucleus (2) is a radius greater thenthat of its convex upper surface (23), the centres of the spheresproviding its two contact surfaces being located on the same axis ofsymmetry (d2) of these two surfaces. On their side, the two platespresent contact surfaces (12, 32) the axes of symmetry (d12, d32) ofwhich are perpendicular to their external faces (10, 30). The horizontaldisplacement part of the nucleus in one direction, due to the rotationon the upper sliding surface around its centre (cs), is compensated by arotation of the nucleus on its lower sliding surface around its centre(ci) which induces horizontal displacement of the nucleus (2) andtherefore of the centre (cs) of the upper sliding surface. The radii ofthe two spheres providing these sliding surfaces (12, 21, 23, 32) aredetermined so as to modify the lateral displacement of the plates bycomparison with each other during their incline. In one embodiment, theradii of these sliding surfaces (12, 21, 23, 32) may be chosen so thatthe movement of the plate is reduced to an incline accompanied with apossible vertical component but without horizontal displacement of theupper plate relative to the lower plate.

[0046] To avoid any risk of ejection of the nucleus (2) during forces inthe inclined position, the latter is kept in its clearance by a centralstop, formed for example by a cylindrical block (4) protruding from theconvex surface of the lower plate and cooperating with edges of a recess(22) arranged in the centre of the contact surface (21) of the lowerconcave surface of the nucleus.

[0047] In one embodiment (FIG. 6a) the lower plate also presents on itsupper face an approximately cylindrical cavity (11) in which the edges(112) protrude from the contact surface (12) with the nucleus (2), andcooperate with the approximately cylindrical perimeter (20) of thisnucleus to ensure an operation of annular stop for it while limiting itsmovement towards the exterior of the contact surface (12) that providesit.

[0048] In one embodiment (FIG. 6a) the internal surfaces of the plates,on their parts (113, 331) exterior to the sliding surfaces, present aform capable of cooperating among themselves to limit by stop theincline of the plates with each other at a determined angle (a1).

[0049] In one embodiment represented in FIG. 7, the stop (4) is providedby the convex surface (12) of the lower plate (1) and presentsapproximately the shape of an inverted cone, that is, its section isgreater in its end (42) opposite the surface (12) that provides it. Bypresenting an undercut shape, the interior surface (224) of the recess(22) cooperates with the exterior surface (40) of the stop (4) to limitthe raising of the nucleus when the latter is in furthest positionagainst this stop (4).

[0050] According to the criteria connected for example to the resistanceof the materials, to the wear and tear or to the kinematics sought, thedifferent shapes and dimensions intervening in the stop mechanisms, forexample exterior (FIGS. 9a and 9 b), annular, central or incline, couldbe determined so as to coordinate the order of arrival at stop of thedifferent parts. These shapes and dimensions could be determined forexample, so that the pieces reach stop at the same stage of movement,for example determined by angular incline (a1) between the lower (1) andupper (3) plates.

[0051] In an embodiment illustrated in FIGS. 7 and 8a, the annular stopoperation is used very little or not at all, which allows the verticalobstruction of the prosthesis to be decreased.

[0052] In an embodiment presented in FIG. 3, the lower surface (21 a) ofthe nucleus (2) may be approximately flat, and then slide on a contactsurface (12 a) of the lower plate (1), also approximately flat. In thisembodiment, the flatness of the contact surface (12 a) of the lowerplate allows the edges (112) of this plate that protrude from thissurface to be particularly effective in their role of annular stop.Therefore, it is possible to manage without the central stop and thus toincrease the common contact surface between the lower plate and thenucleus, which on the one hand, decreases the wear and tear of thepieces and on the other hand, the risk of marking the surface of theplate with placement of the contour of the recess (22, FIG. 6a) in whichis accommodated the central stop (4, FIG. 6a) in other embodiments.

[0053] In an embodiment represented in FIG. 4, the lower plate (1)presents an approximately cylindrical cavity (11) on its upper face theflat bottom (15) of which receives an intermediate piece called block(5). This piece is immobilized in the cavity (11) for example by theedges (112) of this cavity and presents on its upper face a convexsurface (52) on which the lower concave surface (21) of the nucleusslides. This embodiment with the convex surface (52) on which thenucleus slides for example allows the good qualities of the surfacenecessary for the fluidity of movement and longevity of the prosthesisto be obtained more easily and at less cost. It also allows severalmodels to be provided with blocks (5), of different shapes or qualities,that can be chosen in advance or at the time of the surgery according toapplications with the same model of lower plate.

[0054] In an embodiment represented in FIG. 5, the lower plate (1)receives a block (5) in an approximately cylindrical cavity (11)presenting a vertical perforation that the stop (4) integral with thelower plate crosses. On its upper surface, this block supports a convexsurface (52), on which the nucleus (2) and upper plate stack rests.

[0055] As a variant, the stop (4) may be integral with the block (5) onits convex contact surface (52)(FIG. 8b).

[0056] Within the goal of obtaining at rest a corrective effect of therelative position of two vertebrae, the prosthesis may be produced in avariant where the axes of symmetry of the contact surfaces (12, 15, 52,21, 23, 32) or support (10, 30) of one or more pieces are not merged.The pressure (F) exerted by the vertebrae on the two plates in thedirections perpendicular to their external surfaces (10, 30) will thenhave the tendency to induce and continuously maintain an incline (a3,FIGS. 8a, 8 b et 8 c) between these plates (1, 3), that is not zero, forexample in the sense of lordosis.

[0057] An embodiment of such a variant is represented in FIG. 8a wherethe axis of symmetry (d12) of the contact surface (12) of the lowerplate (1) forms an angle (a2) determined with a direction (d10)perpendicular to the external surface of this same lower plate, whilethe axis of symmetry (d32) of the internal contact face (32) of theupper plate (3) is perpendicular to the external surface (30) of thissame upper plate (3). The lower contact surface of the upper plate (3)presents an axis of symmetry parallel to a direction perpendicular tothe support surface (30) of the external face of this same upper plate(3).

[0058] In another variant according to the same principle represented inFIG. 8b, a device is used that includes a lower plate (1) providing ablock (5) the upper contact surface of which (52) presents an axis ofsymmetry (d52) forming an angle (a2) determined with a direction (d51)perpendicular to its lower face (51). The internal contact surfaces (15,32) of the lower (1) and upper (3) plates present axes of symmetryperpendicular to the support surface (10, 30) of their respectiveexternal faces. Thus, at the time of the surgery it is possible tochoose between several blocks (5) with different inclines, according tothe desired degree of correction. This block (5) could be maintainedfixed around an axis perpendicular to the lower plate (1) by any knownmeans (not represented) such as wedge, grooves or complementaryaccidents of shape between the block (5) and the lower plate (1) thatprovides it.

[0059] In another variant according to the same principle, representedin FIG. 8c, it is the nucleus (2) that presents two contact surfaces(21, 23) the axes of symmetry of which (d21, d23) form a determinedangle (a2) between them. The internal contact surfaces (12, 32) of thelower (1) and upper (3) plates present axes of symmetry perpendicular tothe support surface (10, 30) of their respective external faces. Theangular correction (a3) induced by the nucleus (2) could then be keptconstantly in the desired direction relative to the body of the patientby a rotation stop mechanism (not represented in FIG. 8c) of this samenucleus, such a mechanism being described later (FIGS. 9a and 9 b).

[0060] In one embodiment the device according to the invention presentsan exterior stop mechanism, located outside the perimeter of the contactsurfaces of the nucleus (2).

[0061] In a variant represented in FIG. 9a, this mechanism is formed oftwo protruding parts (6) protruding from the cylindrical exteriorsurface of the perimeter of the nucleus (2) in opposite directions. Eachof these protruding parts is held in a housing (162) delimited by twopillars (161) integral with the lower plate (1). These pillars cooperatewith the protruding part (6) or with the surface (20) of the perimeterof the nucleus or both for limiting the movements of this same nucleusin translation as in rotation parallel said plate. The housing issufficiently large to allow small displacements of the nucleus requiredfor the kinematics of the device, while being sufficiently narrow sothat this same nucleus and the lower plate are adjacent in certainpositions, for example, positions of maximum incline of the spinalcolumn. The protruding part (6) or perimeter surface (20) of the nucleus(2) then cooperates with the pillars (161) of the lower plate to retainthis same nucleus and avoid any lateral ejection.

[0062] The pillars (161) present a larger section at the end than at thebase, thus limiting the raising of the nucleus.

[0063] In another operating variant according to the same principle andrepresented in FIG. 9b, this mechanism is formed of two protruding parts(6) protruding from the cylindrical exterior surface (20) of theperimeter of the nucleus (2) in opposite directions. Each of theseprotruding parts presents two arms delimiting a housing (66) which holda pillar (163) integral with the lower plate (1). The pillars (163)present a larger section at their end than at their base.

[0064] These embodiments of stop (9 a and 9 b) may allow the centralstop to be disposed of and to thus increase the contact surfaces whichdecreases the wear and tear. These types of stop (6) are alsoparticularly valuable because of the limitation of the movements of thenucleus in rotation along an axis approximately parallel to the axis ofthe spinal column. In fact, this limitation makes it possible to use acorrective nucleus in which the contact surfaces present axes ofsymmetry that are not parallel, while maintaining in them the correctionin a constant direction relative to the body of the patient.

[0065] In an embodiment represented in FIG. 6a, the lower (1) and upper(3) plates receive means for bony anchoring on their external face,designed to immobilize the prosthesis between the vertebrae or adjacentelements of the spinal column. These anchoring means may be pins (8) orwings presenting a small cross section at their end away from the platethat provides them. These pins then are embedded or are impacted bypunching in the material of the bony elements (V) between which theprosthesis is fitted, for example under the effect of the pressureexerted by the ligaments when the tools are withdrawn, the tools thatkept the vertebrae separated. Driving in the pins in the material of thebony element (V, FIG. 6) then prevents the prosthesis from slidingoutside its site.

[0066] In an embodiment represented in FIG. 1, the plates (1, 3) presentone or more accidents of shape such as notches (7) or perforations (notrepresented) enabling catching of a grasping tool to remove theprosthesis from its site in case of need. The lower plate (1) presents aconvex upper contact surface (12) providing a central stop (4) and acavity presenting edges (112) forming an annular stop.

[0067] In an embodiment represented in FIG. 10, an insertion deviceaccording to the invention is presented in the form of an element (9)called insertion guide, presenting an internal channel (90)approximately rectangular in section in which the prosthesis (P) canslide. This channel (9) is formed from two semi-guides (91, 92) with across section in the shape of a “U”, arranged inversely and fitted intoeach other. At one of the ends, this guide (9) presents one or moreparts called support blocks or edges (910, 920) protruding along itslongitudinal axis (d9). These support blocks (910, 920) form anextension of the walls of the channel called vertical (9) that form thesmall sides of the rectangular section of the channel (9).

[0068] In an application method illustrated in FIGS. 10 and 11, thefitting of the prosthesis device according to the invention is carriedout according to the following steps:

[0069] separating the vertebrae with the aid of known instruments, forexample distraction tools;

[0070] sliding the insertion guide (9)around the distraction tools so asto introduce the support edges (910, 920) between the vertebrae (V);

[0071] release and extraction of the distraction tools, the vertebraebeing kept spread apart by the support edges of the insertion guide;

[0072] introduction of the prosthesis ready for fitting into thechannel, and sliding to near the spinal column;

[0073] adjustment of the incline of the prosthesis according toconformation of the space available between the vertebrae with possibleseparating of the two parts (91, 92) of the channel according to acorresponding angle (a9) to help with this adjustment;

[0074] positioning of the prosthesis in the intervertebral space bypushing by the interior of the channel;

[0075] extraction of the support blocks (910, 920) of the channeloutside the intervertebral space and impacting blocks for bony anchoringin the vertebrae (V).

[0076] In an embodiment illustrated in FIGS. 12a to 14, theinstrumentation used for fitting the prosthesis according to theinvention comprises an insertion guide (93) provided with an internalchannel (90). This channel (90) presents an approximately rectangularcross section, or with a shape approximately complementary to theexterior profile of the prosthesis. This internal channel (90) isprovided with dimensions and shape adequate for allowing the prosthesisto pass and to guide from one of its ends to the other, in a positionand along a displacement approximately parallel to the external faces ofits plates (1, 3). According to the applications, the channel (90) ofthe insertion guide (93) may include scallops in its walls oppositeplates of the prosthesis. Such scallops make it possible to allow theanchoring means (8, 81) to pass provided by the plates of theprosthesis, while guiding the latter sufficiently precisely in thechannel. In the embodiment illustrated here these scallops have theshape of grooves (934, 936) along the axis (d9) of the channel providedby the internal walls of the channel opposite plates (1, 3).

[0077] At one of its ends, called the working end, the walls (931, 932)of the channel (90) perpendicular to the plates of the prosthesis, thatis, located in the plane containing the axis of the spinal column, areextended along the axis (d9) of this channel over a distance determinedso as to protrude relative to the walls of this same channel that areparallel to the plates of the prosthesis. Since these extensions thusform the protruding parts, or support edges, that may be inserted in theintervertebral space to maintain the separation of the plates from thetwo vertebrae surrounding this space.

[0078] The height of these support edges (931, 932) is determined so asto maintain adequate space for allowing the introduction of theprosthesis and its anchoring means (8, 81), according to the method ofanchoring provided. If the anchoring means are formed from sockets (8)or wings (81) before being introduced freely in the space, the supportedges will have sufficient height to allow the height of these socketsor wings to pass. If the anchoring means are formed from wings having topenetrate the vertebral plates by a hollowed trench in the surface ofthese plates and opening laterally, the height of these support edgescould be sufficiently low to allow the height of the prosthesis to passbut not the wings.

[0079] During surgery for fitting such a prosthesis, the surgeon beginsby removing the vertebral disc or its debris, and then uses distractiontools to increase the disc space available between the two vertebraehaving to receive the prosthesis. Such tools are often formed with anelongated handle providing a flat part at the end. This flat end isintroduced between the vertebrae, then it is made to pivot to increasethe separation of the vertebrae.

[0080] In the instrument according to the invention, the internalchannel (90) of the insertion guide (93) is provided to be able to bethreaded around such distraction tools, once they are in place betweenthe vertebrae. Once brought near the spinal column while surrounding thedistraction tools, the insertion guide is pushed so as to introduce itsedges (931, 932) between the vertebrae, in a plane approximatelyparallel to the spinal column. The distraction tools may then be removedfrom the spinal column by making them slide in the channel (90) of theinsertion guide, while the height of the support edges preservessufficient space between the vertebrae to allow fitting of theprosthesis. In the embodiment illustrated here, the insertion guide (93)presents means for interlocking with a guide assembly tool (94), used tobring it near the spinal column and facilitating its fitting. This guideassembly tool (94) is also usable for removing the insertion guide andits support edges, and allowing the vertebrae to tighten on theprosthesis, once the latter is in place.

[0081] Such a guide assembly tool (94) is illustrated in FIGS. 12a and12 b. This tool (94) consists of two elongated tubes (941, 946)articulated to each other by means (945) located at one end, calledassembling, of this tool. These two elongated tubes at their end locatedopposite the assembling end, each provide interlocking means forinsertion guide (93). These interlocking means may comprise, forexample, a hook (942, 947) on each tube (941, 946) the opening of whichis located opposite the other tube. When the guide assembly tool (94) isapproached by the insertion guide (93), the fact of tightening the tubesto each other around their articulation makes it possible for each hook(942, 947) to tightly encircle a tongue (934, 936) in the shape of a “T”protruding on each groove (933, 935) of the insertion guide. Within andin the axis of each tube (941, 946) is found a rod (943, 948) that maybe displaced longitudinally relative to the tubes by screwing meanscomprising a screwing wheel (944, 949). The screwing of these wheelscauses the advance of the rod in the tube and the end of the rodopposite the screwing wheel then comes to lean and block the tongue(934, 936) of the insertion guide (93) within the hook (942, 947)provided by the tube receiving this same rod. This blockage thus makesit possible to interlock the guide to its assembling tool sufficientlystably to make it possible to position said guide around the distractiontools at the spinal column.

[0082] These means (934, 936) of interlocking the insertion guide (93)or others provided by said insertion guide also make it possible toguide and interlock means of approach (95) to this insertion guide.These means (95) of approach include means for positioning theprosthesis, these means of positioning being provided to position andmaintain the assembled prosthesis in a determined position relative tothese means (95) of approach even in the absence of the insertion guide(93). This positioning of the prosthesis on the approach means makes itpossible for the interlocking of the approach means and the insertionguide to put the prosthesis in a position making it possible for it tobe easily displaced from these same means of approach up to in theinternal channel (90) of the insertion guide (93). Thus, it is possibleto prepare the prosthesis in the approach means (95) independently ofthe rest of the operation. Then it is possible to fit the insertionguide on the spinal column without being preoccupied with theprosthesis, then easily and rapidly inserting this prosthesis in theinsertion guide (93) while the latter is already in position against thespinal column.

[0083] As well as illustrated in FIG. 14, these approach means (95)include two shafts (951, 952) connected to each other by articulation(955) so as to come to pinch the prosthesis (P) between two flattenedparts ensuring a determined position of the prosthesis relative to theseapproach means. The ends of these shafts opposite the articulationincluding interlocking means (953, 954) capable of cooperating with theinterlocking means (934, 936) of insertion guide (93) to ensure adetermined position of approach means (95) relative to the insertionguide (93) as well as certain stability to this assembly. At the end ofeach shaft (951, 952), these interlocking means (953, 954) may inparticular comprise a scalloping in which the arms come to encircle theexterior of the groove (933, 935) of the insertion guide while glidingunder the upper bar of the “T” formed by the tongue (934, 936) providedby this same insertion guide.

[0084] Once the insertion guide (93) fitted instead of the distractiontools and the approach means (95) interlocked to this guide, theprosthesis is therefore in a stable position relative to the spinalcolumn, and may be inserted in the insertion guide then slide up to thedisc space. This displacement is achievable here with the aid ofimpacting means, or impactor (96) comprising an impacting end capable ofpressing on the assembled prosthesis, distributed on both plates andwithout touching the nucleus. This impactor includes a central elongatedpart (960) that can be inserted in guiding means as an opening in theshape of a “U” provided by approach means (95) at their articulated end(955). This impactor includes another end (962) called assembling orstriking, that can act to apply a continuous pressure or repeatedshocks, with the hand or by any known tool or apparatus. Such an action,applied on the assembling end (962) of the impactor in the axis (d9) ofthe channel (90) then will be reverberated by the end (961) on theprosthesis, so as to cause its entrance then sliding in the channel (90)of the insertion guide (93), then its insertion or impaction in theintervertebral space.

[0085] In all the prosthesis devices according to the inventiondescribed here, it is necessary to understand that the distinctions of“lower plate” (represented on the bottom of the figures and referenced1) and “upper plate” (represented on the top of the figures andreferenced 3) are above all conventional, the device being able to beused in a different position, even inverse of that consisting of placingthe lower plate toward the bottom of the vertebral column.

[0086] Thus, the invention proposes an intervertebral disc prosthesisdevice comprising at least three pieces, which parts include a plate (1)called lower and a plate (3) called upper (3) producing around at leastone intermediate part called nucleus (2) an articulation by support orsliding between loadbearing surfaces (12, 15, 21, 23, 32) of saidpieces, one of these pieces including at least one protruding part oraccident of shape cooperating with the shape of at least one other ofsaid pieces to form an stop limiting the possibilities of movement ofthe nucleus, characterized in that this stop operation uses at least onestop external to the loadbearing surfaces comprising at least one part(161, 163) protruding from at least one plate (1), located outside theloadbearing surface (12, 15) of said plate and including a face directedtowards the interior of the prosthesis, this face cooperating with aperipheral part (6) of the nucleus (21, 23) situated outside itsloadbearing surfaces (21, 23) and in which the surface is directedtowards the exterior of the nucleus, to limit displacements of thenucleus in translation or in rotation or both in a plane approximatelytransverse to the spinal column.

[0087] According to a particular aspect, the loadbearing surfaces (21,21 a, 23) of the nucleus (2) in contact with the lower plate (1) andupper plate (3) present axes of symmetry (d21, d23, respectively)forming between them a determined angle (a2) that is not zero, so that apressure (F) exerted on the two plates (1, 3) along directionsperpendicular to their external surfaces induces an incline (a3) ofthese plates with each other.

[0088] According to a particular aspect, this external stop limits themovements in rotation of the nucleus (2) relative to at least one plate(1) by contact between parts (6, 161, 163) supporting each other by stopsurfaces, this support being done along a direction approximatelyparallel to the normal of each of these stop surfaces.

[0089] According to a particular aspect, the external stop includes atongue (6) protruding form the nucleus (6) which cooperates with one ofthe plates (1) by confining this tongue (6) in a housing (162) delimitedby pillars (161) protruding from the internal face of this same plate(1) or by a recess (66) separating this tongue into two arms encirclinga pillar (163) protruding from the internal face of this same plate (1),the internal face of a plate being defined at that oriented on the sideof the nucleus.

[0090] According to a particular aspect, the end of at least one pillar(161, 162, 163) presents a section greater than its base, thisenlargement of the pillar cooperating with the shape of the externalstop tongue (6) of the nucleus (2) to limit the raising of this samenucleus relative to the plate (1) providing this pillar.

[0091] In the same spirit, the invention also proposes an intervertebraldisc prosthesis device comprising at least three pieces, including aplate (1) called lower and a plate (3) called upper (3) producing aroundat least one intermediate element called nucleus (2) an articulation bysupport or sliding between loadbearing surfaces (12, 15, 21, 23, 32) ofsaid parts, one of these parts including at least one protruding part oraccident of shape cooperating with the shape of at least one other ofsaid parts to form an stop limiting the possibilities of movement of thenucleus, characterized in that the loadbearing surfaces (21, 21 a, 23)of the nucleus (2) in contact with the lower plate (1) and upper plate(3) present axes of symmetry (d21, d23, respectively) forming betweenthem a determined angle (a2) that is not zero so that a pressure (F)exerted on the two plate (1, 3) along directions perpendicular to theirexternal surfaces induces an incline (a3) of these plates with eachother.

[0092] According to a particular aspect this device is characterized inthat the operation of the stop uses at least one stop external to theloadbearing surfaces comprising at least one part (161, 163) protrudingfrom at least one plate (1) located outside the loadbearing surface (12,15) of said plate and including a face directed towards the interior ofthe prosthesis, this face cooperating with a peripheral part (6) of thenucleus located outside its loadbearing surfaces (21, 23) and in whichthe surface is directed towards the exterior of the nucleus, to limitthe displacements of the nucleus in translation or in rotation or bothin a plane approximately transverse to the spinal column.

[0093] According to a particular aspect, when the two plates have theirexternal faces (10, 30) parallel to each other, their loadbearingsurfaces (12, 12 a, 32) cooperate with the loadbearing surfaces (21, 21a, 23) of the nucleus (2)present axes of symmetry (d12, d32) forming adetermined angle (a4) between them so that a pressure (F) exerted on thetwo plates (1, 3) along directions perpendicular to their external facesinduces an incline (a5) of these plates with each other.

[0094] According to a particular aspect, the loadbearing surfaces (12,32) provided by the internal face of the lower plate (1) and theinternal face of the upper plate (3) are each in complementary contactwith a supporting surface (21, 23, respectively) of the nucleus (2), andeach present a shape, convex and concave, respectively, or inversely,this nucleus itself presenting a perimeter (20) approximatelycylindrical along the axis of symmetry of its contact faces (21, 32).

[0095] According to a particular aspect, the internal face of the lowerplate (1) presents a loadbearing surface (12 a) cooperating with aloadbearing surface (21 a) of the lower face of the nucleus (2), thissame nucleus including on its upper face a convex loadbearing surface(23) in complementary contact with a concave loadbearing surface (32) ofthe internal face of the upper plate (3) the loadbearing surface (12 a)of the internal face of the lower plate being sufficiently extended toallow movement of the nucleus relative to this same lower plate.

[0096] According to a particular aspect, an intermediate element calledblock (5) is added on the internal face of one (1) of the plates andproduces an articulation with the other plate (3) around the nucleus (2)which nucleus presents a concave loadbearing surface (21) and a convexloadbearing surface (23) these two loadbearing surfaces being in contactin a complementary way with one loadbearing surface (52) of the block(5) one, and with a loadbearing surface (32) of the internal face of theplate (3) not including block, for the other.

[0097] According to a particular aspect, the axis of symmetry (d52) ofthe convex loadbearing surface (52) of the block (5) forms a determinedangle (a4) with an axis (d51) perpendicular to its surface (51) withcontact of the plate (1) so that a pressure (F) exerted on the twoplates (1, 3) along directions perpendicular to their external facesinduces an incline (a5) of the plates with each other.

[0098] According to a particular aspect, at least one of the loadbearingsurfaces (12, 52, 21, 23, 32) allowing articulation has a shape makingup part of a sphere.

[0099] According to a particular aspect, the loadbearing surfaces of thetwo faces of the nucleus (2) have shapes making up parts of a sphere,the face presenting a concave loadbearing surface (21) having a radiusgreater than that of the face presenting a convex loadbearing surface(23).

[0100] According to a particular aspect, each of the plates (1, 3)includes on its external face one or more protruding parts with smallsection forming a bony anchoring, these protruding parts coming to beembedded or impacted in the surface of contiguous bony elements (V)under the effect of pressure, once the prosthesis is in position betweentwo vertebrae or bony elements.

[0101] According to a particular aspect, one or more of the pieces ofthe prosthesis include accidents of shape, notches (7) or perforationslikely to see a tool again to facilitate the extraction of saidprosthesis.

[0102] According to a particular aspect, the plates (1, 3) are composedof an alloy with base of stainless steel with cobalt-chromium and thenucleus (2) has polyethylene base.

[0103] In the same spirit, the invention proposes instrumentation forinserting or fitting the prosthesis according to one of claims 1 to 15characterized in that it comprises an insertion guide (9,93) includingan internal channel (90) presenting an end in which certain edges orsupport edges (910, 920, 931, 932), protrude from the others along thelongitudinal axis (d9) of the channel so as to be able to take the placeof distraction tools of a known type previously used to increase theopening of the disc space, this channel (90) presenting an internalsection capable of surrounding these same distraction tools while theymaintain this opening, then allowing their extraction through saidchannel while said support edges (910, 920, 931, 932), for their part,preserve the opening of the disc space by replacing the distractiontools, then receiving and guiding the prosthesis (P) for insertion inthis disc space.

[0104] According to a particular aspect, the internal channel (90)presents an approximately rectangular section or with a shapeapproximately complementary to the exterior profile of the prosthesis,taken in a section along the plane perpendicular to the direction ofinsertion.

[0105] According to a particular aspect, the support edges (931, 932) ofinsertion guide (93) form an extension of the channel (90) walls locatedon a plane containing the axis of the spinal column.

[0106] According to a particular aspect, the insertion guide (9) isformed from at least two elements (91, 92) separated along one or moreplanes parallel to the longitudinal axis (d9) of the channel, theseparts each including at least one portion of the transverse section ofthe channel and being able to be spread apart according to a determinedangle (a9) and allowing the introduction and sliding of the prosthesis(P) in the channel.

[0107] According to a particular aspect, the internal surface of thechannel (90) on its walls opposite external faces of the plates (1, 3)of the prosthesis (P), includes at least one groove (913, 914) allowingthe passage of protruding parts (8, 81) for anchoring provided by theseplates during displacement of the prosthesis in this channel (90).

[0108] According to a particular aspect, the instrumentation comprisesapproach means (95) of the prosthesis capable of receiving theprosthesis and of maintaining with it all the different components,these approach means (95) being able to be connected by interlockingmeans to the insertion guide (93) so as to present the prosthesis at theentrance of the channel (90) in a position appropriate for allowing itsentrance into this channel (90).

[0109] According to a particular aspect, the instruments comprisesinsertion means, called impactor (96) of the prosthesis in the channel(90) of the insertion guide (93) then into the disc space, this impactorbeing guided by the support means (95) so as to be in contact with theprosthesis in its part opposite the entrance of the channel (90), thisimpactor (96) being able to apply or transmit a pressure or repeatedshocks to the prosthesis to cause its sliding in the channel, then itsinsertion in the disc space.

[0110] According to a particular aspect, the support means include twoshafts (951, 952) connected by an axis to a assembling end (955), theseshafts being able to be closed up to pinch the prosthesis (P) betweenthem and to maintain it so assembled, these two shafts each providingconnection means to the guide for use (93), this connection thenmaintaining these two shafts closed up on the prosthesis.

[0111] It must be obvious for those skilled in the art that the presentinvention allows embodiments in numerous other specific forms withoutgoing far from the field of application of the invention as claimed. Asa result, the present embodiments must be considered by way ofillustration, but may be modified in the field defined by the scope ofthe attached claims, and the invention must not be limited to detailsgiven above.

1-25. (canceled)
 26. Intervertebral disc prosthesis device comprising atleast three pieces, including a lower plate, an upper plate and anucleus between the upper and lower plates, said pieces being arrangedto provide an articulation by support or sliding between load bearingsurfaces of said pieces, one of said pieces including at least oneprotruding part or shape cooperating with the shape of at least oneother of said parts to form a stop arrangement for limiting movement ofthe nucleus, the stop arrangement including at least one stop elementexternal to the load bearing surfaces, the external stop element havingat least one part protruding from at least one plate located outside theload bearing surface of said plate and including a face directed towardsthe interior of the prosthesis, the face arranged to cooperate with aperipheral part of the nucleus being situated outside load bearingsurfaces of the face and in which the face is directed towards theexterior of the nucleus, to limit displacement of the nucleus intranslation or in rotation or both in a plane approximately transverseto the spinal column.
 27. Device according to claim 26 wherein the loadbearing surfaces of the nucleus in contact with the lower plate andupper plate have axes of symmetry, the axes of symmetry intersecting ata determined non-zero angle in the nucleus so that a pressure adapted tobe exerted on the two plates along directions perpendicular to externalsurfaces of the plates causes the plates to be inclined with respect toeach other.
 28. Device according to claim 26 wherein the external stopelement is arranged to limit rotational movement of the nucleus relativeto at least one of the plates by contact between parts supporting eachother by stop surfaces, this support resulting from the contact beingalong a direction approximately parallel to the normal of each of thestop surfaces.
 29. Device according to claim 26 wherein the externalstop includes a tongue protruding from the nucleus, the tongue beingadapted to be inserted into one of the plates by a tongue confiningstructure including a housing delimited by pillars protruding from theinternal face of said one plate or by a recess separating the tongueinto two arms encircling a pillar protruding from the internal face ofsaid one plate, the internal face of said one plate being the faceoriented on the side of the nucleus.
 30. Device according to claim 26wherein at least one pillar has a tapered cross section, so an end ofthe pillar has a cross section greater than its base, the tapered shapeof the pillar cooperating with the shape of the external stop tongue ofthe nucleus to limit lifting of the nucleus relative to the plateincluding the tapered pillar.
 31. Intervertebral disc prosthesis devicecomprising at least three pieces, including a lower plate, an upperplate and a nucleus between the upper and lower plates, said piecesbeing arranged to provide an articulation by support or sliding betweenload bearing surfaces of said pieces, one of said pieces including atleast one protruding part or shape cooperating with the shape of atleast one other of said parts to form a stop arrangement for limitingmovement of the nucleus, the load bearing surfaces of the nucleus incontact with the lower plate and upper plate having axes of symmetry,the axes of symmetry intersecting at a determined non-zero angle in thenucleus so that a pressure adapted to be exerted on the two plates alongdirections perpendicular to external surfaces of the plates causes theplates to be inclined with respect to each other.
 32. Device accordingto claim 31 further including at least one stop external to the loadbearing surfaces, the external stop having at least one part protrudingfrom at least one plate located outside the load bearing surface of saidplate and including a face directed towards the interior of theprosthesis, the face arranged to cooperate with a peripheral part of thenucleus being situated outside load bearing surfaces of the face and inwhich the face is directed towards the exterior of the nucleus, to limitdisplacement of the nucleus in translation or in rotation or both in aplane approximately transverse to the spinal column.
 33. Deviceaccording to claim 26 wherein the plates are arranged so that inresponse to the external faces thereof being parallel to each other, theload bearing surfaces of the plates cooperate with the load bearingsurfaces of the nucleus to provide axes of symmetry intersecting at adetermined angle between them so that a pressure exerted on the platesalong directions perpendicular to the external surfaces thereof causesthe plates to be inclined with respect to each other.
 34. Deviceaccording to claim 26 wherein the load bearing surfaces on the internalface of the lower plate and the internal face of the upper plate areeach in complementary contact with a supporting surface of the nucleusand each of the load bearing surfaces on the internal face of the lowerplate and the internal face of the upper plate have a shape, convex andconcave, respectively, or inversely, the nucleus having an approximatelycylindrical perimeter along the axis of symmetry of its contact faces.35. Device according to claim 26 wherein the internal face of the lowerplate has a load bearing surface cooperating with a load bearing surfaceof the lower face of the nucleus, the nucleus including on its uppersurface a convex load bearing surface in complementary contact with aconcave supporting surface of the internal face of the upper plate, theload bearing surface of the internal face of the lower plate beingsufficiently extended to allow movement of the nucleus relative to thelower plate.
 36. Device according to claim 26 further including anintermediate block on the internal face of one of the plates forproviding an articulation with the other plate around the nucleus, thenucleus having a concave load bearing surface and a convex load bearingsurface, the concave and convex load bearing surfaces of the nucleusbeing respectively in complementary contact with a convex load bearingsurface of the block, and with a concave load bearing surface of theinternal face of the plate.
 37. Device according to claim 36 wherein theaxis of symmetry of the convex load bearing surface of the block forms adetermined angle with an axis perpendicular to its surface, contactbetween the block and the plate being such that a pressure exerted onthe plates along directions perpendicular to the external faces of theplates causes the plates to be inclined with respect to each other. 38.Device according to claim 26 wherein at least one of the load bearingsurfaces for allowing articulation has a shape corresponding with asegment of a sphere.
 39. Device according to claim 26 wherein the loadbearing surfaces of the two faces of the nucleus have shapescorresponding with segments of a sphere, one of the plates having a loadbearing face having a concave load bearing surface having a radiusgreater than a convex load bearing surface of the other plate. 40.Device according to claim 26 wherein each of the plates includes on itsexternal face one or more protruding parts with a small section forminga bony anchoring, these protruding parts being embedded or impacted inthe surface of contiguous bony elements under the effect of pressure,while the prosthesis is in position between two vertebrae or bonyelements.
 41. Device according to claim 26 wherein one or more of thepieces of the prosthesis has a shape, notches or perforations tofacilitate extraction of said prosthesis by a tool.
 42. Device accordingto claim 26 wherein the plates are formed of an alloy with a base ofstainless steel with cobalt-chromium and the nucleus has a polyethylenebase.
 43. Instrumentation device for inserting or fitting the prosthesisaccording to claim 26, the instrumentation device comprising aninsertion guide including an internal channel having an end includingedges protruding from the end along the longitudinal axis of the channelso as to be able to receive distraction tools of a known type used toincrease the opening of the disc space, the channel having an internalsection capable of surrounding the distraction tools while they maintainthe opening for enabling extraction of the distraction tools throughsaid channel while said protruding edges maintain the opening of thedisc space by replacing the distraction tools, then receiving andguiding the prosthesis for insertion in the disc space. 44.Instrumentation device for fitting the prosthesis according to claim 43wherein the internal channel has an approximately rectangular crosssection or a shape approximately complementary to the exterior profileof the prosthesis, taken in a section along the plane perpendicular tothe direction of insertion.
 45. Instrumentation device for fitting theprosthesis according to claim 43 wherein the protruding edges of theinsertion guide form an extension of the channel walls located in aplane containing the axis of the spinal column.
 46. Instrumentationdevice for fitting the prosthesis according to claim 43 wherein theinsertion guide is formed from at least two elements located in one ormore planes parallel to the longitudinal axis of the channel, each ofthe elements of the insertion guide including at least one portion of atransverse section of the channel and being able to be spread apart by adetermined angle for allowing the introduction and sliding of theprosthesis in the channel.
 47. Instrumentation device for fitting theprosthesis according to claim 43 wherein the internal surface of thechannel on its walls adapted to be opposite external faces of the platesof the prosthesis includes at least one groove allowing the passage ofat least one protruding part on at least one of the plates of theprosthesis for anchoring the at least one plate during displacement ofthe prosthesis in the channel.
 48. Instrumentation device for fittingthe prosthesis according to claim 43 further comprising a holder for theprosthesis for receiving the prosthesis and for maintaining theprosthesis with all the different components in a stable state, theholder being able to be connected by an interlock to the insertion guideto enable the prosthesis to be placed at the entrance of the channel ina position appropriate for enabling the prosthesis to enter the channel.49. Instrumentation device for fitting the prosthesis according to claim43 further comprising an impactor for inserting the prosthesis into thechannel of the insertion guide and for then inserting the prosthesisinto the disk space, the impactor being arranged to be guided by asupport so as to contact a part of the prosthesis opposite the entranceof the channel, the impactor being able to apply or transmit a pressureor repeated shocks to the prosthesis to cause its sliding in the channelthen its insertion in the disc space.
 50. Instrumentation device forfitting the prosthesis according to claim 43 further including a supportfor holding the prosthesis at the channel entrance, the supportincluding two shafts connected to turn about an axis of an assemblingend of the instrumentation device, the shafts being able to be closed topinch the prosthesis between them and to maintain the prosthesis in anassembled condition, the shafts each providing a connection to a guidefor inserting the prosthesis into the channel, the connection beingarranged to maintain the two shafts closed on the prosthesis.
 51. Deviceaccording to claim 31 wherein the plates are arranged so that inresponse to the external faces thereof being parallel to each other, theload bearing surfaces of the plates cooperate with the load bearingsurfaces of the nucleus to provide axes of symmetry intersecting at adetermined angle between them so that a pressure exerted on the platesalong directions perpendicular to the external surfaces thereof causesthe plates to be inclined with respect to each other.
 52. Deviceaccording to claim 31 wherein the load bearing surfaces on the internalface of the lower plate and the internal face of the upper plate areeach in complementary contact with a supporting surface of the nucleusand each of the load bearing surfaces on the internal face of the lowerplate and the internal face of the upper plate have a shape, convex andconcave, respectively, or inversely, the nucleus having an approximatelycylindrical perimeter along the axis of symmetry of its contact faces.53. Device according to claim 31 wherein the internal face of the lowerplate has a load bearing surface cooperating with a load bearing surfaceof the lower face of the nucleus, the nucleus including on its uppersurface a convex load bearing surface in complementary contact with aconcave supporting surface of the internal face of the upper plate, theload bearing surface of the internal face of the lower plate beingsufficiently extended to allow movement of the nucleus relative to thelower plate.
 54. Device according to claim 31 further including anintermediate block on the internal face of one of the plates forproviding an articulation with the other plate around the nucleus, thenucleus having a concave load bearing surface and a convex load bearingsurface, the concave and convex load bearing surfaces of the nucleusbeing respectively in complementary contact with a convex load bearingsurface of the block, and with a concave load bearing surface of theinternal face of the plate.
 55. Device according to claim 54 wherein theaxis of symmetry of the convex load bearing surface of the block forms adetermined angle with an axis perpendicular to its surface, contactbetween the block and the plate being such that a pressure exerted onthe plates along directions perpendicular to the external faces of theplates causes the plates to be inclined with respect to each other. 56.Device according to claim 31 wherein at least one of the load bearingsurfaces for allowing articulation has a shape corresponding with asegment of a sphere.
 57. Device according to claim 31 wherein the loadbearing surfaces of the two faces of the nucleus have shapescorresponding with segments of a sphere, one of the plates having a loadbearing face having a concave load bearing surface having a radiusgreater than a convex load bearing surface of the other plate. 58.Device according to claim 31 wherein each of the plates includes on itsexternal face one or more protruding parts with a small section forminga bony anchoring, these protruding parts being embedded or impacted inthe surface of contiguous bony elements under the effect of pressure,while the prosthesis is in position between two vertebrae or bonyelements.
 59. Device according to claim 31 wherein one or more of thepieces of the prosthesis has a shape, notches or perforations tofacilitate extraction of said prosthesis by a tool.
 60. Device accordingto claim 31 wherein the plates are formed of an alloy with a base ofstainless steel with cobalt-chromium and the nucleus has a polyethylenebase.
 61. Instrumentation device for inserting or fitting the prosthesisaccording to claim 31, the instrumentation device comprising aninsertion guide including an internal channel having an end includingedges protruding from the end along the longitudinal axis of the channelso as to be able to receive distraction tools of a known type used toincrease the opening of the disc space, the channel having an internalsection capable of surrounding the distraction tools while they maintainthe opening for enabling extraction of the distraction tools throughsaid channel while said protruding edges maintain the opening of thedisc space by replacing the distraction tools, then receiving andguiding the prosthesis for insertion in the disc space. 62.Instrumentation device for fitting the prosthesis according to claim 61wherein the internal channel has an approximately rectangular crosssection or a shape approximately complementary to the exterior profileof the prosthesis, taken in a section along the plane perpendicular tothe direction of insertion.
 63. Instrumentation device for fitting theprosthesis according to claim 61 wherein the protruding edges of theinsertion guide form an extension of the channel walls located in aplane containing the axis of the spinal column.
 64. Instrumentationdevice for fitting the prosthesis according to claim 61 wherein theinsertion guide is formed from at least two elements located in one ormore planes parallel to the longitudinal axis of the channel, each ofthe elements of the insertion guide including at least one portion of atransverse section of the channel and being able to be spread apart by adetermined angle for allowing the introduction and sliding of theprosthesis in the channel.
 65. Instrumentation device for fitting theprosthesis according to claim 61 wherein the internal surface of thechannel on its walls adapted to be opposite external faces of the platesof the prosthesis includes at least one groove allowing the passage ofat least one protruding part on at least one of the plates of theprosthesis for anchoring the at least one plate during displacement ofthe prosthesis in the channel.
 66. Instrumentation device for fittingthe prosthesis according to claim 61 further comprising a holder for theprosthesis for receiving the prosthesis and for maintaining theprosthesis with all the different components in a stable state, theholder being able to be connected by an interlock to the insertion guideto enable the prosthesis to be placed at the entrance of the channel ina position appropriate for enabling the prosthesis to enter the channel.67. Instrumentation device for fitting the prosthesis according to claim61 further comprising an impactor for inserting the prosthesis into thechannel of the insertion guide and for then inserting the prosthesisinto the disk space, the impactor being arranged to be guided by asupport so as to contact a part of the prosthesis opposite the entranceof the channel, the impactor being able to apply or transmit a pressureor repeated shocks to the prosthesis to cause its sliding in the channelthen its insertion in the disc space.
 68. Instrumentation device forfitting the prosthesis according to claim 61 further including a supportfor holding the prosthesis at the channel entrance, the supportincluding two shafts connected to turn about an axis of an assemblingend of the instrumentation device, the shafts being able to be closed topinch the prosthesis between them and to maintain the prosthesis in anassembled condition, the shafts each providing a connection to a guidefor inserting the prosthesis into the channel, the connection beingarranged to maintain the two shafts closed on the prosthesis.